No. It's got several distinctly different characteristics, you can tell
an awful lot about the quality of the engine and ignition system with
the spark signal.

What kind of current is there? Does the
current create the spark and then return through the same cable?

I just hooked a split core current transformer with 3000 windings
around a
spark plug cable and got nothing. I'm trying to re-create a signal
similar
to that which a timing light would use.

Then get a hold of a timing light clamp and see how it's done.

Get a hold of a clamp on EMI filter, wind ~ten turns of enamelled copper
wire around one half of the ferrite and then attach a scope to the ends
of the ECW, see what sort of signal you get out. I guarantee it's not a
'simple' pulse.

Really, I would like to just know when this engine is on and off
without
any lag. I also don't want to shutdown the engine to install it.

Tap into the crank sensor, tap into the ignition coil LT drive signal or
the injector drive (assuming it uses fuel injection).

I had success using hall effect sensors on fuel injector bodies and also
on ignition coils, extremely easy to deal with and also logic compatible
if you pick the right one although a simple comparator circuit worked
best as it was adjustable to suit.

Plenty of ways to tell if an engine is running that are simpler to
interface to and measure than a spark plug lead.

Relevant Pages

Re: Monitor Automotive Spark Plug?... I suppose the electronic ignition systems can ... tailor the pulse to whatever is required. ...transient event.... would be a better way to tap into the spark plug signal....(comp.arch.embedded)

Re: 96 yamaha bravo no SPARK... I tested all switches, they ok, multimeter says ignition coil is ... good, spark plug cap is good, spark plug is good. ... Only things left are the stator coil and cdi....(rec.sport.snowmobiles)

Qualcast Lawn mower...tecumseh engine but i don't know what the model number is of the engine ...spark plug so i checked the spark plug and it had a very weak spark so ... had points but it don't just a ignition coil so it looks like i will ...oil but in the manual it says use SAE 30 oil but after searching the web ...(uk.rec.gardening)